Bringing Soundweb greens back to live

We are still using quite a lot of  old green Soundwebs 9088 and 9088ii in our soundprojects. The main reason being  that these ancient machines were allready capable of some FIR filtering.
Mind you: there is a bug in the software which makes you have to reverse the filter kernels. Presumably nobody ever noticed using linear phase filters (symmetrical as these will be) ;)

Anyway I had some broken ones lying around so I thought it would be time to do some repairing.
One of the apparent vulnerabilities is the power supply cap marked as C216.
So after replacing these I was able to get some off them back to live.
For all you out there plagued by the dreaded searching.... (at infinitum) modus I will repeat some 'rules':

1. replace C216 cap, while you are at it maybe it's a good idea to upgrade cap C265 with something beafier as well.
2. use the spare jumper at the option A position to set your machine in debug modus.
3. switch on power, you now should get the 'nightrider' row of flashing leds.
4. use the backup loader.exe to reload the firmware. make shure you have the correct *.a21 file. I learned the hard way do not to make a mistake!
5. when done switch of power, replace jumper and reboot.

As allways use correct settings of com ports and bitrate (38400 front, 115200 back). Also the FTDI driver / USBtoRS232 works fine on windowsXP (and 7) but on windows 8 it appears to be troublesome.

Now for the fun (and utterly time consuming and by no means commercially viable) part.
Let see if we can do some 'audiophile' modifications.
In the issue 1 model (9088) there are some VCA IC's build in to facilitade volume controle directly after the DAC's.
These suck! ;)
I forgot the type number but in a earlier experiment some years ago I removed these and  shortened the signal path. So no more volme controle on the output and maybe (with high gain power amps) a bit excessive noise.
But hey, who cares for noise?
It's the universe coming through our speakers!
Big plus!

Next thing I thought would be whorthwhile is replacing all these (non-polar) caps in the signal path.
Well this wasn't going to happen.
All my regular dope dealers like Farnell and RS and the like seem to have stopped selling these, hmmm, bummer.
Now what if we replaced them with regular caps back to back with a DC bias.
(This is an idea I actually stole from a very old Midas PRO4 console I once owned).

Big improvement?
Argh euuhh, yes with all my skills I can notice the difference (some more clarity) but I 'm not even shure if this is desirable.
So, nah not going to do that on all our machines...

 ...edit...edit...edit...
Not completily convinced by the dispointing results of the above modification I decided to give it a second try.
Same mod but this time I tested a stereo a/b comparison..wow.. this is some serious shit.. much broader and deeper image and a very convincing musical impact..now why the hell is this???

LouReed with new carbon cone speakers

This summer the shipment of our brand new carbon fiber speakers finally arrived.

The first listening test worked out quite promising, so we decided to upgrade our LouReed systems with these babies.

Nico is going to use a set of these speakers for some complicated acoustic performances during itgwo , so the design goal of the adjusted filters would have an emphasis  on producing a clear natural sound.

As opposed to rocking your guts with e.g. Rammstein, that is.

Probably Sebastiaan will call this boring (I guess) :)

By looking at the speaker you might expect a really full bottom-end with long excursion bangs of the speaker like 'car' hifi speakers do.

Not so!

Fortunately in this case 'cause that would bring also a lot of intermodulation distortion. Think thumping yourself on the chest while singing. Not looking for that in this case.

So why a rubber surround? 

As is the case with al stiff materials in speaker design, shurely they sound a lot better: stiffer cone -> stiffer piston movement -> less break up distortion.

But when they do breakup (and at at 'our' levels they always do): HORROR.

Remember the 2' titanium vs 2' aluminium driver diafragm 'upgrade' problems?

Or the special sound of that A brand line-array with yellow speakers for everything, when you hit it real hard?

Well here comes the genius of our Chinese friends: the rubber surround will absorb those hard breakup modi! Brilliant!

 

I also tested a other speaker in the same cabinet.

From the front the cone looks like your standard 12' (guitar) speaker.

Soundwise this gives you that nice zzhangg you are looking for in metal guitar a la Rammstein.

Not that pak-pak from a modern plastic coated speaker (think 'french' PA's).

So what's the Chinese ingenuity here? Back Coating! 

Al the advantages of a stiffer cone by coating without the ugly breakup. Again brilliant!

So in fact we now have two recipes for our LouReed systems

Does this mean a different magnitude/phase slopes of the overall response?

No, certainly not, actually the final results show quite simular curves.

Does this mean different EQ needed to match or linearise the responses?

No, also certainly not, actually in both designs zero EQ was applied.

(to the speaker that is)

Shurely, different program material makes me want to apply different micro EQ (no more then 3 dB, Q<2, that is), but I always end up in bypassing them again.

Which will have to bring me to the next topic:

Distortion matching as a design goal in loudspeaker tuning

oh, euh, yes, by the way: all the time we are talking distortion here I mean that very-fine-grained-hardly-noticeble but still quite -important-emotion-wise effect for which I don't know how to quantify else then by using my ears...

Valid dual FFT measurement

On several instances last week I have been talking to people how to acquire valid  dual FFT measurements.
It really stroke my how much miss understanding there still floats about, so here we go:
Crash course measurements in KBLsystems-style:

First::
Dual FFT means we can finally get rid of that annoying pink/white noise at terrorising levels.
Just use your favorite music!
As long as it contains enough spectral content it will be a perfect source and you can use both eye and ear in your system tuning.
Keep a keen eye on your coherence tracer to see if your program material works.

Second:
Surely you can use the 'delay finder' function to find the overall time difference between the reference signal and the measurement signal, but be aware that all software will make this snap to the maximum of the impulse response which can be
a) quite challenging when the IR is smeared over time e.a. in a filtered sub respons
b)  will yield the 'wrong' phase response

Let me elaborate the latter:

 

This represents a close mic measurement of mid speaker. Clearly one can see the low end magnitude roll-off and it's associated phase behavior of a small speaker in a closed cabinet.

In the following picture the above graph shows  the IR with the delay finder nicely snapped to the maximum of the IR:

We will now show you why this is wrong.

The high end roll-off in magnitude which is (partly) due to the inductance of the voice coil should also find its counterpart in phase behavior. But in above graph one is to believed that this would not be the case.

Next picture is a simulation I made:

 

The black ine is the imported measurement and the red line is a constructed model based on this measurement.

The thin red line show the associated (min.) phase behavior.

So the measured phase should look like this. In fact the thin black line all ready shows the 'correct' trend.

Now how do we acquire this?

Simple! 

Adjust the delay finder by hand to the ONSET of the impulse response:

Tada!

Valid measurement!

Now bust your heads on what I 'm actually doing here <grin> ;)